Acoustic silencers or pulsation dampeners have been known for many years. The most common type comprises a shell defining a volume divided in the middle with a tube connecting the two compartments. The smaller the tube in diameter and the longer its length, the more impedance, or in acoustical terms, the more inertence is developed. Also, the smaller the tube and the longer it is, the higher the friction losses. Some of the earlier pulsation dampeners in order to have long tubes without restricting the flow too much, install a hairpin design so that the tube is longer than the vessel or shell, and the tubes are doubled back on each end.
Other methods for developing acceptable reduction in noise were to belmouth the ends of the tubes and install a venturi diffuser on the exit ends so that the pressure drop is minimized, allowing higher velocity, smaller tubes and therefore a higher inertence.
Other prior art devices include structures such as shown in my U.S. Pat. No. 2,993,559 which employs three chambers interconnected by various tubes in such a manner as to effect in addition to attenuation, phase cancellation of acoustic waves.
In all of these prior art designs, it is normally desirable that the tube within the shell be relatively small in diameter and long in length. The tubes are thus "limber" as compared to short fatter tubes and normally require intermediate supports fastening the tube within the shell of the acoustic filter. Where the acoustic noise to be dampened includes low frequency components as result, for example, from reciprocating compressors, the low frequency pulsations tend to dilate the shell resulting in failure of the tube supports either at the shell or at the tube. The long tube design is desirable in order to introduce a proper amount of linear inertence, but as a consequence, as noted, such design has made prior art silencers and dampeners expensive to manufacture and of questionable reliability after prolonged use.